1. Field of the Invention
The present invention relates to a method of making grating having an anti-slip coating.
2. Background Art
Grating is used as a flooring surface in many applications. Typical applications for grating include platforms and trench covers that may be used, for example, at chemical plants, waste water treatment facilities, oil derricks, and for many other applications. Anti-slip surfaces are beneficial in many applications where grating is used as a flooring surface especially if the surface is wet or coated with oil or grease. When persons work on, or vehicles drive over, grating that is used as a flooring surface, they may slip on the surface unless it has anti-slip coating applied to the top surface of the grating.
Applicant previously proposed a method for applying a non-skid coating to metal bars in U.S. Pat. No. 4,618,511. Several methods of applying a non-skid coating are disclosed in the '511 patent. The first method is to assemble a series of bearing bars together side by side with spacers between adjacent bearing bars. The spacers are made of a material that does not accept metallic spray particles and yet is capable of withstanding heat from the metal spray. The second method does not require spacers between adjacent bars but requires arrangement of the bars in a vertically stacked relationship relative to each other such that the end surfaces are offset from each other. The side surfaces of the bars may have a thin oil film to resist metal spray adherence to the side surfaces. A third approach is to provide a drive mechanism that engages alternate bars and moves the bars relative to each other during the spray coating application. The drive mechanism reciprocates the alternate bars longitudinally while the coating is being sprayed to inhibit bridging of spray coating material between adjacent bars. Alternatively, the bars could be moved in a vertical relative motion that would be perpendicular to the above-described longitudinal movement.
Applicant's prior solution proposed in the '511 patent was never widely adopted for the manufacture of non-skid grating. Instead, grating having a non-skid coating was provided by arc-spraying fully assembled sections of grating. To increase productivity, with appropriate size grating, the grating could be double stacked wherein the metal spray coating would be applied to two sections of fully assembled grating at the same time with the bearing bars being staggered to allow for application of the metal spray to the top surfaces of both of the stacked grating sections. While this method provides an excellent anti-slip grating product, a substantial amount of the metal spray is wasted. The wire used to form a high hardness anti-slip surface is a relatively expensive cored wire. If the metal spray created by the arc-spray process does not contact the top of the bearing bars, it is wasted as over spray that adheres to the sides of the bearing bars or the coating machine's work supporting surfaces.
The '511 patent focused on the concept of spreading grit over the surface and then coating the grit to bond it to the metal supporting surface. When the '511 patent was filed, it was believed that an anti-slip surface could not be applied to adjacent bars without spacers or relatively moving the bars because the weld spray tends to form a layer that bridges between adjacent bars. If spacers are used between adjacent bars, costs are incurred for the spacers and for labor required to assemble the bars and spacers together as disclosed in the '511 patent.
If the bars are assembled into a special fixture having a motor drive that is capable of moving the bars longitudinally or vertically, substantial capital costs are incurred for the fixture and labor costs are incurred for assembling the bars to the fixture. Motor drives, required to move the bars relative to each other, are required to operate in a harsh environment that may cause premature failure of the motor drive. Elaborate fixtures become coated with the anti-slip coating and may require maintenance to remove over spray deposits from the fixtures prior to reuse.
There is a need for a cost-effective method of making slip resistant grating. There is also a need to reduce wasted material lost in over spray when the anti-slip coating is applied to grating having relatively large open areas compared to the area of the bars to be coated that form the walking and working surface. There is also a need to reduce the labor required to manufacture anti-slip grating products. There is a further need for a method of making anti-slip grating that can be used to manufacture any style of grating and grating made of aluminum, steel, stainless steel or fiberglass.
The present invention is directed to solving the above problems and fulfilling the needs as outlined above. The present invention is summarized below.